Microwave harmonic generator utilizing self-resonant ferrite



1, 1970 l. KAUFMAN ETAL 3,544,880

MICROWAVE HARMONIC (IENERA'I'OR UTILIZING SELF-RESONANT FERRITE FiledAug. 9. 1968 c p JVX rurrlte um M '43 25 35 21 -27 V Ferrite DielectricI 7 lrvmg Koufmon 9' Richard E.N0r'ron INVENTORS BY 41s. a, W,

ATTORNEY United States Patent 3,544,880 MICROWAVE HARMONIC GENERATORUTILIZ- ING SELF-RESONANT FERRITE Irving Kaufman, Tempe, Ariz., andRichard E. Norton, Beverly Hills, Calif., assignors to TRW Inc., RedondoBeach, Calif., a corporation of Ohio Filed Aug. 9, 1968, Ser. No.751,424 Int. Cl. H02m 5/06; H03f 7/00 US. Cl. 321-69 8 Claims ABSTRACTOF THE DISCLOSURE A microwave generator for developing a harmonic suchas the second harmonic of a signal input frequency. The harmonicgenerator utilizes an element exhibiting ferrimagnetic resonance such asa piece of ferrite or else a ferroelectric element. The ferrite elementis so dimensioned that it will resonant electromagnetically at thedesired harmonic frequency. On the other hand, a magnetic field appliedto the ferrite element has a magnitude to provide gyromagnetic resonanceat the fundamental frequency. As a result, substantially all the energyat the desired harmonic is contained in the ferrite element.

BACKGROUND OF THE INVENTION This invention relates generally tomicrowave generators, and particularly relates to a harmonic generatorhaving a relatively large energy output at a desired harmonic frequency.

Harmonic generators at microwave frequencies are well known in the art.They usually include a circuit such as a chamber or waveguide resonantat the fundamental or input frequency as well as at the desired outputfrequency which is a harmonic of the input frequency. It can becalculated that in that case the output power is given by the followingequation:

wherein P is the input power,

F is a figure of merit of the material, such as a ferrite,

w is the angular input frequency,

P is the desired output power at the second harmonic,

and

R is a quantity which must be minimized to achieve maximum output power.

In turn, the quantity R may be defined as follows:

2coU one; (2)

wherein k is the amplitude of the magnetic field at the second harmonicfrequency in the resonant structure,

U is the energy stored in the electromagnetic field at the secondharmonic frequency corresponding to the magnetic field k and Q is theunloaded Q of the resonant circuit at the second harmonic frequency.

.The above formulas have been obtained by equalizing the power generatedto the power lost in the harmonic cavity of relatively large sizecontaining a piece of ferrite of very small size. The reason for thesmall ferrite is that alarge piece disturbs the field configuration tothe point of rendering the scheme ineffective.

The scheme of a large resonator and a small specimen "of ferrite iscontrary to what is desired, according to Equations 1 and 2. For thereone sees a quantity R which should be as small as possible for maximumpower output and at constant frequency w and constant resonator Q. R isproportional to the energy stored in the electromagnetic field when themaximum amplitude of the h-component electromagnetic field is h Thus, Ris minimized (and P is maximized) when U is minimized. And to minimizeU, we minimize the resonator volume.

It is accordingly an object of the present invention to provide aharmonic generator at microwave frequencies which will deliver aharmonic output frequency at a relatively high energy.

Another object of the present invention is to provide a microwavefrequency doubler wherein the energy at the desired second harmonicfrequency is substantially entirely contained in a ferrite element.

A further object of the present invention is to provide a microwavefrequency multiplier which may be realized with either an isotropic oranisotropic ferrite element.

SUMMARY OF THE INVENTION A microwave frequency multiplier in accordancewith the present invention includes signal input means tuned to thefrequency of the desired input signal. An element which exhibitsferrimagnetic or ferroelectric resonance such as a ferrite element isdisposed in the resonant chamber. Such an element normally hasdielectric properties at harmonics of the signal frequency. The ferriteelement is so dimensioned that it will resonate at the desired harmonicfrequency. In other words, its dimensions are such as to establish astanding electromagnetic wave at the desired harmonic frequency which issubstantially contained in the element. On the other hand, a steadymagnetic field is established through the element which has a magnitudeto provide gyromagnetic resonance of the ferrite element at the signalfrequency.

The output wave at the desired harmonic such as the second harmonic ofthe fundamental frequency may be obtained by any suitable output circuitmeans. This may, for example, consist of a loop coupled to theelectromagnetic field at the desired harmonic of the signal frequencydeveloped by the element. Alternatively, a tuned waveguide may be usedas the output circuit means.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and method of operation, aswell as additional objects and advantages thereof, will best beunderstood from the following description when read in connection withthe accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic top plan view ofa microwave frequency doubler in accordance with the present invention,utilizing a disk of isotropic ferrite:

FIG. 2 is a side elevational view taken on lines 22 of FIG. 1 andillustrating particularly the ferrite in its resonant chamber and theoutput loop probe:

FIGS. 3a and 3b are respectively a top plan and side elevational view ofthe ferrite disk of FIGS. 1 and 2 illustrating the dipole resonancethereof;

FIG. 4 is a schematic top plan view taken in lines 4--4 of FIG. 5 ofanother embodiment of a microwave frequency doubler embodying theinvention and utilizing an anisotropic ferrite rod;

FIG. 5 is a side elevational view of the frequency doubler of FIG. 4;

FIG. 6 is an enlarged side view of the anisotropic ferrite rod and itsend plates, showing particularly the magnetic field at the secondharmonic frequency; and

FIG. 7 is a side elevational view similar to that of FIG. 6, of amodification of the frequency doubler of FIG. 4 utilizing both a ferriteand a dielectric rod.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingwherein like elements are designated by the same reference characters,and particularly to FIGS. 1 and 2, there is illustrated a microwavefrequency multiplier embodying the present invention. The embodiment ofFIGS. 1 and 2 is based on the fact that a specimen of materialexhibiting ferrimagnetic resonance can be made to act as a dielectric ata harmonic of the fundamental frequency, and hence can be made into aharmonic resonant. The embodiment of the invention of FIGS. 1 and 2utilizes isotropic ferrite.

There is provided a waveguide which is provided with a conventionaltuning device, such as one or more tuning screws 9 that cause virtuallyall of the input power at the frequency w to be absorbed by a ferriteelement 11. The input signal is impressed by a source not shown on thewaveguide 10. This is indicated by P representing the input power at theangular frequency to. If desired, a resonant chamber may be used;however, it may not be necessary to use a resonant chamber provided theferrite element is comparatively large compared to the size of theresonant structure.

A disk 11 of a material which exhibits ferrimagnetic resonance such as apiece of ferrite having isotropic properties may be used. It is alsofeasible, however, to utilize instead an element having ferroelectricproperties. The ferrite may, for example, consist of yttrium irongarnet. Two magnets 12 and 13, having magnetic north and south poles asshown, are disposed to generate a magnetic field H which extends atright angles to the axis of ferrite disk 11 as shown by the dashed lines14. Preferably the magnitude of the steady magnetic field H developed bythe magnets 12 and 13 may be adjusted to provide magnetic resonance inthe ferrite disk 11 at the desired input frequency.

A loop probe 15 is disposed in the neighborhood of disk 11 and may be amagnetic probe as shown for coupling to the magnetic field at theharmonic frequency developed about the ferrite disk 11. The wires 16 ofthe probe 15 extend through waveguide 10 through a suitable aperture 17.

Preferably, as shown in FIG. 2, the flat ends of the disk 11 are coveredby a pair of conductive plates 18.

In order to explain the operation of the frequency doubler of FIGS. 1and 2, reference is also made to FIGS. 3:: and 3b. As explained before,the steady magnetic field H extends at right angles to the axis of thedisk 11 and through the flat ends of the ferrite disk 11. On the otherhand, the alternating magnetic field hdeveloped by the micro-wave inputsignal also extends in the flat plane of the disk 11 as shown by thedashed lines 20. Accordingly the two magnetic fields H and h,,, areorthogonal to each other.

It should be noted that the strength or magnitude of the magnetic fieldH is such as to provide gyromagnetic resonance of the ferrite disk 11 atthe input or signal frequency. Since the gyromagnetic resonance extendsover only a small frequency range, it will be evident that there is nogyromagnetic resonance at harmonics of the fundamental or signal inputfrequency. Accordingly the ferrite disk 11 behaves like a dielectric atharmonics of the fundamental frequency.

Further in accordance with the invention the ferrimagnetic disk 11 is soproportioned that it is in electromagnetic resonance at 2w, that is, attwice the fundamental frequency or some other desired harmonicfrequency. The magnetic field lines for k are also shown in FIG. 1 bydashed lines 21. It will be seen that the magnetic field lines at thesecond harmonic frequency are orthogonal to the magnetic field h andhence parallel to the steady magnetic field at the flat surface offerrite disk 11. It should also be noted that the second harmonicmagnetization m also appears parallel to H. The harmonic magnetization mis proportional to h,,, where h is the field intensity at the inputfrequency. It is due to this m that the second harmonic magnetizationacts as a source at the frequency 2w.

The second harmonic magnetization m excites a resonance at the secondharmonic frequency so that a standing electromagnetic wave at the secondharmonic frequency is set up. As stated before, the loop 15 couples tothe magnetic field. However it should be emphasized that the use of anelectric probe which couples to the electric field existing at rightangles to the magnetic field is also feasible.

The resonance which is excited by the second harmonic magnetization isthe dipolar mode as shown in FIGS. 3a and 3b. Here the electric fieldvector is indicated by E and the magnetic field by h.

It will now be apparent that the metallic plates 18 which cover theouter flat surfaces of the disk 11 serve the purpose to limit theelectric field and to allow resonance in the so-called dipolar mode.

In order to cause the disk 11 to resonate at the second harmonicmagnetization, its diameter D is determined by the following relation:

wherein a is the free-space wavelength of the second harmonic frequencywithin the ferrite, and a, is the dielectric constant of the ferrite atthe resonant frequency.

To summarize again, the embodiment of FIGS. 1 and 2 utilizes a magneticfield having such a magnitude as to permit the ferrite disk 11 to havegyromagnetic resonance at the signal frequency. On the other hand, thedisk 11 is so dimensioned to establish a standing electromagnetic waveat the desired harmonic of the input signal frequency. This may, forexample, be the dipolar mode shown in FIGS. 3a and 3b, in which case thediameter is determined by Formula 3.

Referring now to FIGS. 4 through 6, there is illustrated anotherembodiment of a microwave frequency multiplier in accordance with thepresent invention. This frequency multiplier utilizes a rod ofanisotropic ferrite where the length of the cylinder or rod determinesthe dipolar dielectric mode which causes the ferrite to resonate at thedesired harmonic frequency.

Thus there is an input waveguide 10 which is again tuned to the signalinput frequency. This is indicated in FIG. 4 by P indicating the inputpower at the angular input frequency w. Again the two magnets 12 and 13providing respectively north and south poles as shown are disposed inthe manner shown in FIG. 5. A rod or cylinder 25 of anisotropic planarferrite material is disposed in the waveguide 10 in such a manner thatthe steady magnetic field H is parallel to the axis of the rod 25. Themagnitude of the magnetic fieldvis again such as to provide gyromagneticresonance of the rod 25 at the signal input frequency. g

The rod 25 is preferably cut in such a manner that the easy plane ofmagnetization is parallel to the axis of the rod, that is, parallel to HThe magnetic field h at the signal input frequency is shown by thedashedlines 26 and extends at right angles to the axis of the rod through theflat ends of the rod.

As shown particularly in FIG. 6, the flat surfacesof the rod 25 may becovered again with metallic plates 27. Again their purpose is toterminate the electric field within the rod 25. V

The second harmonic magnetization m w is now also parallel to the axisof the rod 25 and the resulting magnetic field h w is shown in FIG. 6 at28. Preferably the length of the rod 25 is one-half of the guidewavelength of this dipolar dielectric mode set up in the rod. Again wemust consider the ferrite as a dielectric at the harmonic of thefundamental frequency.

The desired output wave at the harmonic such as the second harmonic ofthe signal frequency may be coupled out by a waveguide 30 which is tunedto the desired second harmonic. This is indicated by P at 2w. A couplinghole 31 couples the ferrite rod 25 to the output waveguide 30. However,it will be understood that the output power may be obtained in any othersuitable manner.

Accordingly it will be evident that use is now made of the dipolarpropagating dielectric mode of the ferrite rod 25 at the desiredharmonic. Again the gyromagnetic resonance at the signal frequency isdetermined by the strength of the magnetic field H On the other hand,the ferrite which now is a dielectric at any harmonic frequency is madeto resonate at the desired harmonic frequency by making the length ofthe cylinder 25 approximately onehalf of the guide wavelength of thedipolar propagating dielectric mode. In other words, this is one-halfthe wavelength at the desired harmonic frequency in the ferrite.

While the embodiment of the invention shown in FIG. 6 shows a basicscheme for a ferrite resonator, the modification of FIG. 7 may bepreferred. If the magnetic field h driving the ferrite is everywhere inphase across the ferrite material, then the harmonic magnetization mwill also be in the phase across the material. The dipolar mode of ahalf-wave resonator however has a harmonic magnetic field k of oppositephase at its two outer metallic ends. In view of this situation, notmuch power is generated at the second harmonic frequency unless half ofthe rod is deactivated magnetically. This can be achieved with theembodiment shown in FIG. 7. Here the ferrite rod 25 is combined with adielectric rod 35 which preferably has the same diameter. Again the twoopposed or free ends are covered by a pair of metallic plates 27 asshown. All that is needed is to use the structure of FIG. 7 for thatshown in FIG. 6 and to insert it into the waveguide 10 as shown in FIGS.4 and 5.

There has thus been disclosed a microwave frequency multiplier such as afrequency doubler making use of a material having ferrimagneticresonance. This may be a piece of ferrite of either isotropic oranisotropic properties. The magnetic field is so adjusted that it causesferrimagnetic resonance of the ferrite element at the fundamental orsignal input frequency. A desired harmonic is set up in the ferrite bydimensioning it so that a standing electromagnetic wave is set up in theelement at a selected harmonic of the fundamental frequency. Sincesubstantially all of the harmonic energy is now contained in the ferriteelement, the energy output at the desired harmonic is substantiallyhigher than that of prior art devices.

What is claimed is:

1. A microwave frequency doubler comprising:

an input waveguide tuned to the frequency of a desired input signal,said waveguide being not resonant at the second harmonic of said inputsignal frequency;

a disk of isotropic ferrite disposed in said waveguide and having adiameter selected to resonate at said second harmonic;

conductive plates covering the flat surfaces of said disk;

means for establishing a steady magnetic field substantially at rightangles to the axis of said disk, said magnetic field having a magnitudeto provide gyromagnetic resonance of said disk at said input signalfrequency; and

a loop probe coupled to the electromagnetic field at said harmonic ofsaid input signal frequency for deriving the doubled frequency outputwave.

2. A frequency doubler as defined in claim 1 wherein said loop probe isa magnetic probe coupled to the magnetic field at said harmonicfrequency.

3. A microwave frequency doubler comprising:

a signal input waveguide tuned to the frequency of a desired inputsignal, said input waveguide having dimensions smaller than necessary tocause said waveguide to resonate at the second harmonic of said inputfrequency;

a rod disposed in said waveguide, said rod consisting of anisotropicferrite, said rod having dimensions selected to cause said element toresonate at said second harmonic and said dimensions being of the sameorder of magnitude as those of said waveguide;

conductive plates covering the flat surfaces of said ferrite rod;

means for establishing a steady magnetic field substantially parallel tothe axis of said rod, said magnetic field having a magnitude to providegyromagnetic resonance of said element at said input signal frequency;and

output circuit means coupled to said ferrite rod for deriving thedoubled frequency output Wave.

4. A frequency doubler as defined in claim 3 wherein said ferrite rodhas a length substantially one half wavelength of the guide wavelengthat said harmonic frequency.

5. A frequency doubler as defined in claim 3 wherein said anisotropicferrite is cut so that the easy plane of magnetization is parallel tothe axis thereof.

6. A frequency doubler as defined in claim 3 wherein a rod of dielectricis disposed adjacent to said ferrite rod, both of said rods havingsubstantially the same diameter.

7. A frequency doubler as defined in claim 6 wherein the outer flatsurfaces of said ferrite rod and of said dielectric rod are covered byconductive plates.

8. A frequency doubler as defined in claim 6 wherein said ferrite rodhas a length substantially one half wavelength of the guide wavelengthat said harmonic frequency.

References Cited UNITED STATES PATENTS 2,890,422 6/1959 Schlicke 33383X3,041,524 6/1962 Karayianis et a1. 321-69 3,165,690 1/1965 Kaufman321-69 3,260,852 7/1966 Heiter 307-88.3 3,300,729 1/1967 Chang 3304.8X

OTHER REFERENCES Proceedings of the IRE, October 1956; vol. 44, No. 10,pp. 1239 and 12941297.

J D MILLER, Primary Examiner G. GOLDBERG, Assistant Examiner s. c1. X.R.30788.3; 330 4.s

